Transcript Energy - jpsaos

Stephen pulls David at constant
speed upward along a frictionless
water slide.
Which of the following statements
best describes the situation?
System
40o
Earth
1 The energy in the system changes. This change is equal to the force
that Stephen exerts on David multiplied by the distance David moves.
2 The energy in the system changes. This change is equal to the force
that Stephen exerts on David multiplied by the distance David moves
multiplied by the cos 40o.
3 David is moving at a constant speed, thus the net force exerted on
David is zero. Zero net force means zero work. Thus, the energy of the
system does not change.
A situation is described with a bar chart and in words.
Which verbal description matches this bar chart?
Kinitial + Ug initial + Us initial
+
W = Kfinal + Ug final + Us final +DEint
1 An object fell off a cliff and the energy in the system was
transferred from gravitational potential energy to kinetic energy.
2 A spring on a table shot an object. You measured the kinetic
energy of the object when it landed at the same elevation.
3 A spring shot an object vertically from a height above the ground.
You then measure the kinetic energy at ground level just before the
ball hits the ground.
A situation is represented pictorially below. Which bar
chart best matches the picture?
system
y
t, y = h
ti, yi = 0
v = constant
Earth
Ko +
1
2
3
Ugo
W
K + Ug + Us
Tim is carrying a basket of laundry to be washed. This motion
is represented by a free body diagram and a motion diagram.
y

Fhand on basket

v = constant
x

Fearth on basket
Earth
Which verbal description best
matches the diagrams? (The
earth and basket are the system)
1
Since the basket is moving, work is done on the basket and that is all
we are able to tell.
2
Tim does work, but the systems energy does not change.
3
The velocity is constant, the height is constant and Tim is doing work.
The internal energy of the system must be increasing.
4
No work is being done on the system which implies the system’s
energy does not change.
Alan is on a frictionless kiddie coaster.
Which energy bar chart
best matches this
situation as the car
goes to the bottom?
1
2
Ki + Ugi W = Kf + Ugf
Ki + Ugi W = Kf + Ugf
h>hf >0
vf >0
3
hi=h
vi=0
Ki + Ugi W = Kf + Ugf
If the same coaster was
not frictionless, which
bar chart would
describe that process?
1
Ki + Ugi W = Kf + Ugf + DE
2 Ki + Ugi W = Kf + Ugf + DE 3
h>hf >0
vf >0
hi=h
vi=0
Ki + Ugi W = Kf + Ugf
A roller coaster car’s trip is described by the
energy bar chart shown below.
Ki + Ugi W = Kf + Ugf
Which final point in the
picture below matches
the bar chart?
Initial
1 Final
3 Final
y
2 Final
5 Final
0
4 Final
The energy bar chart below represents a car’s
motion.
Ki + Ugi W = Kf + DE
Which motion diagram matches this
situation?
1

vfinal
3
vfinal

vinitial

vinitial
2

vfinal

vinitial

4
vinitial vfinal  0
A car is moving horizontally as described by
the motion diagram below.

vfinal

vinitial
Which energy bar chart best matches this?
1
Ki + Ugi W = Kf + Ugf
2
Ki + Ugi W = Kf + Ugf
3
Ki + Ugi W = Kf + Ugf
4
Ki + Ugi W = Kf + Ugf
Tim is moving a basket of laundry and his hands
exert a force on the basket equal in magnitude to
the force of the Earth on the basket.
Which energy bar chart(s) could match this situation?
(The earth and basket are the system)
1
3
5
Ki + Ugi W = Kf + Ugf
Ki + Ugi W = Kf + Ugf
3&4
2
4
6
Ki + Ugi W = Kf + Ugf
Ki + Ugi W = Kf + Ugf
2, 3 & 4